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Full text of "Circuits"

Game Show Buttons 



Make] Projects 

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build, hack, tweak, share, discover,- 



Game Show Buttons 

Written By: Steve Hobley 



PARTS: 



Resistor. 500-piece assortment. 1/4 Watt (1) 

from RadioShack. Available in the parts drawers at your local RadioShack. Plenty of 

resistors for future projects! 

High-Brightness LED red (2) 
from RadioShack. 

555 Timer IC (2) 

Breadboard Wire Kit (1) 
from RadioShack. 

6" Modular IC Breadboard (1) 
from RadioShack. 

Quad OR Gate (74HC32) (1) 

SPTD Submini Toggle Switch (1) 
from RadioShack. 

Pushbutton (2) 
from RadioShack. 

Capacitor ceramic 0.01 |iF (2) 
from RadioShack. 

NPN transistors, 15 pack (1) 
from RadioShack. 



© Make Projects www.makeprojects.com Page 1 of 5 



Game Show Buttons 



SUMMARY 

In this project, taken from Charles Piatt's book Make: Electronics , we're going to breadboard 
a fairly complex circuit using 555 timers and an OR logic gate. 

Using these and some other, common components, we'll build a game show button system. 
When one button is pressed, it automatically locks the other one out, until the quizmaster 
flips a reset switch. 

"OR gates" are one of several types of basic logic gates. The logic of ORs are, as the name 
suggests, if input A or B is true (on), output X is true (on); thus, in this design, if either 
player presses his or her push button, the circuit will go true (on), locking out the other 
player's button, and can only be reset via the toggle switch. This circuit is ideal for two- 
person quiz contests! 

"I'll take 'Cool Projects' for 100, Alex!" 



Step 1 — Gather Your Parts, Install ICs and Hookup Wire 










• Gather together the required parts along with the breadboard. 

• Breadboards have positive and negative power rails running along the top and 
bottom. They are typically marked with a red line for positive (+) and blue (or black) 
line for negative (-). When you power the board, you can connect a 5-6v battery (or DC 
power supply) with positive and negative connected to the respective rails. 

• Our first task is to place the 3 ICs (integrated circuits) in line, and be sure they're in the 
correct orientation. Using the 22AWG jumper wire, connect power (- is black, + is red). 
You can see that I've connected to the two power rails on either side of the breadboard. 

• The next step is to add the additional lines to power and ground (third image), again using 
red for positive, and black for negative. 

© Make Projects www.makeprojects.com Page 2 of 5 



Game Show Buttons 



Step 2 — Install Buttons, Switch, and Resistors 



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• Connect the three 10KQ 1/4 watt resistors, the SPDT toggle switch (white wires), and 2 
push buttons (yellow wires). 

• Add two wires to connect the middle 10KQ resistor to the 555 timers. The longer wire will 
connect to the first 555 IC, and the shorter wire will jump this connection to the second 555 
IC (image 2, yellow wires). 

• Seen in image 3, we've connected the push buttons to the OR-gate inputs via the white 
wires. 

Step 3 — Add Capacitors and Make More Wire Connections 



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• Continue adding more connections (yellow wires) between the OR-gates on the logic chip 
(image 1). 

• In image 2, we've added the two 0.01 F ceramic disc capacitors - these go from the lower 
negative power rail, and pin 2 of each 555 timer. 

• In the final picture, we hooked up two white wires to connect the ceramic disc caps back 
to the logic chip. 



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www.makeprojects.com 



Page 3 of 5 



Game Show Buttons 



Step 4 — Add LEDs and Finish Your Connections 



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• Now get out your LEDs! The longer leg of the LED is the positive (anode) leg - the shorter 
leg is negative (cathode). In our next step, we'll connect the anode to the ICs output, while 
the cathode will connect to a 330Q resistor and then on to ground. 

• Place the two red indicator LEDs and 330Q resistors. Finally wire the LEDs to the 555 ICs 
with 2 red wires (image 1). 

• Our last connections! Two black wires feed the signal from the LEDs back into the OR- 
gate logic chip (image 2). 

• That's it! Connect up a 5-6v power supply to the breadboard power rails and test it out. 
Here's a video showing how the circuit operates: http://www.youtube.com/watch? 
v=pQC6SLnlc... 



Step 5 — Addendum: The Schematic 



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• Here is the full schematic for the 
game show buttons. 



© Make Projects 



www.makeprojects.com 



Page 4 of 5 



Game Show Buttons 

This project demonstrates that it's possible to implement complex time-dependent circuitry 
without relying on a microcontroller or computer. 

The 555 timer IC is one of the most useful components available, and here we've used it in a 
latching configuration. 

This document was last generated on 201 2-1 1 -03 03:50:54 AM. 



© Make Projects www.makeprojects.com Page 5 of 5